1. Field of the Invention
The present invention relates to systems and methods for electrically interconnecting circuit boards, and in particular to a system and method for transmitting high power through a flexible circuit interconnect from the edge of a printed circuit board, through multiple coaxial interconnects, to a power regulator board, all within a reduced form factor.
2. Description of the Related Art
As processing speeds continue to increase, the power demands of the processors used in such systems (such as microprocessors for servers and desktop systems) have increased dramatically. While patent applications referenced above have shown that it is desirable to mount power conversion modules (which convert higher voltage signals to low voltage-high current power signals) close to the devices that have high power dissipation requirements, it is often difficult to do so due to thermal, mechanical and other constraints.
One reason for this difficulty is that the power in such devices often requires large heatsinks which encroach on the power conversion modules and forces the power conversion to be further away then desired. Thus, what often results is a fairly high dynamic voltage drop across the interconnection of the power interconnect, due to high slew-rate switching of the load, typically resulting in false switching of the device itself which may corrupt data. Therefore, it is seen that there is a need to bring both the power regulation closer to the load while maintaining a low impedance, small form factor, and easy to assemble construction which is of reasonably low cost. The present invention satisfies that need.
To address the requirements described above, the present invention discloses a method and apparatus for electrically interconnecting a first circuit board having a power conditioning circuit and a second circuit board having a power dissipating component disposed therebelow along a z (vertical) axis. In an illustrative embodiment, the apparatus comprises a first flexible circuit having a first set of raised conductive contacts, the first flexible circuit disposed on a first side of the second circuit board; and a second flexible circuit having a second set of raised conductive contacts, the second flexible circuit disposed on a second side of the second circuit board opposing the first side of the second circuit board. A power signal from the power conditioning circuit is provided to the second circuit board at least in part by either the first set of raised conductive contacts on the first flexible circuit or the second set of raised conductive contacts on the second flexible circuit. Further, a ground return is provided to the second circuit board by the set of raised conductive contacts that are not used to provide the power signal from the power conditioning circuit to the second circuit board.
The present invention therefore can be described by a power interconnecting structure between a power regulator board and the card edge connector of an interposer board which houses a high performance microprocessor using a low impedance, low cost, flexible circuit. The housing may be made of molded plastic and the flexible circuits may be single-sided. The flexible circuit has multiple coaxial interconnects which interconnect to a power regulator module mounted directly above the edge-card interface of the interposer or the flexible circuit can connect directly to the power module without the intervention of the coaxial interconnects. A substrate may be mounted between or on the flexible circuits for interconnect to the coaxial connectors or the connection may be made directly to the flexible circuits themselves. The coaxial interconnects can be disconnectable at the flexible circuit side or the power module interface or may be permanently attached to both sides. Pressure to the edge card contact region on the interposer is maintained through either an elastomeric pad residing within the housing or through spring fingers located in the same area as the elastomer which maintains a constant force for a high conductivity electrical connection by pressing against the back of the flexible circuit opposite the side the bumps are located. Low electrical impedance is maintained by keeping the separation between the flexible circuits very small throughout the design. The electrical connection between the power regulator module and interposer requires very little space and maintains a very low electrical impedance while compacting the overall construction by placing the integrated power regulator module above the interposer itself. The unit also is designed where the flexible circuits compensate for mechanical tolerances in the stackup relieving forces from being applied to the interposer and its associated thermal interface.